In encapsulation of a semiconductor device (hereinafter also referred to as the package) by transfer molding, a problem of wire sweep has heretofore been pointed out, and in compliance with changes in package shapes, measures for optimization of molding conditions, a reduction of viscosity in a resin composition for encapsulating a semiconductor (hereinafter also referred to as the resin composition) and the like have been taken. However, in recent trend, on the one hand, for a semiconductor device, fine pitch wire bonding and finer wiring of wires have been advanced by finer wiring in a semiconductor element (hereinafter also referred to as the element or the chip) for the purposes of higher functionality and cost reduction, and accordingly more wire sweep has easily occurred than ever before. On the other hand, with the progress of improvement of the reliability in a semiconductor device and high filling of a filler for the purpose of a reduction of warpage in BGA (Ball Grid Array), further viscosity reduction of a resin composition becomes difficult, and measures with respect to wire sweep have been more difficult than ever before. In addition, moldability failure in welding or the like has easily occurred due to narrow gap formation right above the chip caused by thinning of packages and elements made into multiple stages, and molded MAP (mold array package) formation.
In the compression molding technique, the flow rate of a resin is remarkably lower and flow in the lateral direction is smaller, as compared to transfer molding which has been widely used for encapsulation of a semiconductor, so that wire sweep hardly occurs and the compression molding technique is a powerful measure for the above fine pitching. Furthermore, the compression molding technique is an excellent molding method with respect to filling of a narrow gap portion right above the chip in which welding according to the molding method hardly takes place, is a molding method suitable for fine pitching and thinning of a semiconductor device to be developed hereafter, and is expected to be widely applied hereafter.
As a method for obtaining a semiconductor device obtained by encapsulating a semiconductor element by compression molding using a resin composition for encapsulating a semiconductor, there have been proposed a method including using a granular resin composition (for example, refer to Patent Document 1), and a method including using a sheet-like resin composition (for example, refer to Patent Documents 2 and 3).
In case of the method including using a granular resin composition, there was a need to carry out conveyance and weighing of the resin composition before the granular resin composition was put into a cavity of a compression mold installed in a compression molding machine. However, according to the method described in Patent Document 1, relatively large granules having a size of about 2 mm were used, so that weighing accuracy was not sufficient in some cases.
Meanwhile, the granular resin composition put into the cavity of the compression mold installed in the compression molding machine was melted in the cavity by closing the mold using the compression molding machine, and was filled in the whole cavity. However, at this time, the degree of wire sweep and filling properties of the narrow gap portion right above the chip were depending on the melt viscosity of the melted resin composition and the way of progress of curing thereof.
In Patent Document 3, for the purpose of reduction in wire sweep, there has been proposed that the melt viscosity and the gel time of the resin were in the specific range, but this method related to a method including using the resin processed into a sheet form, and the melt viscosity of the melted resin composition and the way of progress of curing have not been proposed in compression molding using the granular resin composition.